// @flow

// Deep freeze an object by using a Proxy.
// This is better than Object.freeze() as we can create coherent error messages
// and easily only deliver frozen subobjects when they are accessed. We can
// even add custom logic, like warning if you access a property that doesn't exist.
/* eslint-disable no-console */
export default function deepFreeze<T>(inputObj: T, options: {get: boolean, set: boolean} = {get: true, set: true}): $ReadOnly<{|...T|}> {
  // Our handler that rejects any change to the object and any nested objects inside it
  const deepFreezer = {};
  if (options.get) {
    deepFreezer.get = function get<T: Object>(obj: T, prop: $Keys<T>, _receiver: Proxy<T>) {
      // Clone w/o Proxy
      if (prop === 'toJSON') return () => obj;
      // If dealing with nested object, nest the proxy untill it reaches the direct property of it's parent proxy
      if (typeof obj[prop] === 'object' && obj[prop] !== null) {
        return new Proxy(obj[prop], deepFreezer);
      }
      // If prop is directly accessible, just do the default operation
      else {
        if (!(prop in obj) && prop !== 'length' && prop !== '__esModule' && typeof prop !== 'symbol') {
          throw new Error(`Can not get unknown prop "${String(prop)}" on frozen object.`);
        }
        return obj[prop];
      }
    };
  }
  if (options.set) {
    deepFreezer.set = function set<T>(obj: T, prop: string, _val: any, _rec: Proxy<T>): boolean {
      throw new Error(`Can not set unknown prop "${prop}" on frozen object.`);
    };
  }
  // $FlowIgnore for all useful purposes the output type is T here
  return new Proxy(inputObj, deepFreezer);
}